Cellulose ether solutions and method of spinning the same



unsatisfactory products. ,duction of shaped articles having improved prop- -metal trithiocarbonate.

Patented Mar. 13,1951

CELLULOSE ETHER SOLUTIONS AND METHOD OF SPINNING THE SAME Norman Louis Cox, Claymont, DeL, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 9, 1947, Serial No. 759,899

21 Claims.

This invention relates to the coagulation of cellulose ethers from caustic solutions. More particularly, it relates to a new process for manufacturing cellulose ether articles, such as filaments, films, caps, bands, and ribbons, having modified and improved properties.

It is known that cellulose ethers containing a suificient number of ether groups such as hydroxyethyl-, carboxymethyb, or methoxy groups may be dissolved in caustic and the solution spun into acid-salt coagulating baths to form filaments or films. The resulting gel elements are always highly swollen and lead to harsh,

Methods for the proerties are, therefore, desirable.

An object of this invention is to improve the production of various articles from cellulose ethers. A further object is the coagulation of alkaline solutions of cellulose ethers in a manner which keeps the primary gel swelling at a low level. A still further object is the improvement in stretchability, water resistance and other properties of articles prepared from cellulose ethers. pear hereinafter.

These objectives are accomplished in general by extruding into coagulating baths containing sulfuric acid, zinc sulfate and sodium sulfate alkaline solutions of cellulose ethers to which solutions has been added at least 1.0%, based on the weight of the solution, of a water-soluble Preferably, the alkaline solution of cellulose ether and the watersoluble metal trithiocarbonate. is extruded in contact with between 0.2% and 1% (based on the weight of the solution) of a basic nitrogencus modifier selected from the group consisting of alkali-soluble monoamines or their quaternary ammonium salts, said amines or quaternary ammonium salts having at least four: carbon atoms and containing no radical or more than seven carbon atoms. The desired contact may be obtained by incorporating the basic nitrogenous modifiers in the alkaline solutions: of the ethers or in the spinning baths.

The invention will be more clearly understood by referring to the examples and discussion which follow. The gel swelling values given be low for the yarn samples were all determined according to the following procedure. The gel thread is collected as a single layer on a bobbin 3.5 inches in diameter by manually operating a traverse mechanism with the thread being stretched 80% in the hot secondary bath. The

Other objects of the invention will apsample is centrifuged (1400 R. P. M.) for a minute, cut off, and weighed in a closed bottle. The sample is washed free of acid, dried in an oven at C. and weighed. The ratio of the gel weight to the cellulose weight (grams of gel per gram of cellulose) is referred to as the gel swelling. In the case of films, small sections of gel film are cut off, blotted, between pulp sheets and weighed. After determination of the cellulose content, gel swelling values are determined as above for filaments.

Besides gel swelling another important indication of the quality of the structures is the rate of neutralization in filaments and films during coagulation. This rate is determined by adding to the caustic solution of the cellulose derivatives a suitable indicator, such as bromcresol purple (pH range 5.2 to 6.8) and observing in the case of filaments the distance in inches from the spinneret at which the purple color completely disappears; in the case of films, the time in seconds for the purple color to disappear is recorded. The use of a water-soluble trithiocarbonate in the caustic solutions of cellulose ethers and the addition of basic nitrogenous compounds to the caustic solution or the coagulating bath reduces the rate of neutralization of the spinning filaments over that of the unmodified systems. It has been found that, in general, the slower the rate of neutralization, the lower the gel swelling and. the better the yarn properties. The decreased neutralization rate is believed to indicate that the modifying agents of this. invention permit greater dehydration of the solution before the gel structure of the filament or film is permanently set.

The following examples are given for illustrative purposes and are not to be considered limitative.

EXAMPLE I Hydroxyethyl cellulose containing 0.1 hydroxyethyl group per glucose unit (just enoughsubstitution to produce caustic solubility) was dissolved in caustic by vigorously mixing after subjecting the mixture to repeated freezing and thawing actions. A solution containing 4.5% hydroxyethyl cellulose, 6% caustic, and 1.3% sodium trithiocarbonate with a trace of bromcresol purple indicator was prepared in this manner. The filtered solution was poured on a glass plate and spread to a thickness of .015 The plate was immersed in a coagulating bath containing 6% sulfuric acid, 14% sodium sulfate, and 10% zinc sulfate at 50 C. for five minutes. Time in seconds for the blue color of the indicator in the solution to disappear was clocked and after five mintues, the film was removed from the coagulating bath, blotted and weighed 4, these important factors which lead to improved film strength.

for gel swelling determination. It can be seen Table HI in Table I below that the rate of neutralization 5 of the film and the gel swelling were reduced as Qiggfi; 53%;; compared to values for fihns prepared from a -9B O teo Neusimilar hydroxyethel cellulose solution containg fiifi ggfi 3:53: 3? gfi ing no sodium trithiocarbonate. Addition of ammonium ybenzyltrimethylammonium chloride to the 1o droxde) agulating bath further reduced gel swelling and rate of neutralization. In addition it will be ob- @31 served that films from modified solutions have 1 -8 measurably improved film tenacities. This indicates that the quality and the physical properl ties of films and filaments are important func- EXAMPLE IV tions of the gel shrinkage. Two solutions of the sodium salt of carboxy- Table I Solution Ingredi- N i Gel fi gg fi fif g f Hgo i 2 df z 04 Swelling ggjggg 4. 5- 10-14-10 11 9. 1 240 4. 5-6-1. 3 10-14-10 19 7. e 343 4.561.3 10-14-10+1% benzyltrime- 31 6.1 561 thylammonium chloride EXAMPLE II methyl cellulose (0.75 mol of substitution per glucose unit and a viscosity of 500 centipoises for g i gggg g fia z 32?? as? a 2 aqueous solution by the falling ball method) caustic containing sodium trithiocarbonate to were pteparedpy d1 sso1vmg salt sodnflm produce a hydroxyethyl ceuu1Os hydloxideand 1n scc l1um hydroxide modified with NaOH-% NazCSa) solution. The ether dissolved 35 13% sodmm i i z Solutlons very readily in caustic at (l-10 C. After filterwere prepared by f t the mgredlents [thoring and deaerating, the solution was spun into ougply for an F11.ms w plate cast 100 filament, 275 denier yarn on an apparatus lowlpig the methq'd desct'lbgcl m Example The similar to a commercial bobbin machine, the addlplon of q i tnthlocaljbonate gave apspinning speed being 880 inches per minute. The 40 p1 eclable reductlon m gel Swenmg' aqueous coagulating bath contained 6% H2S04, Tab e IV 14% NazSO4 and 15% ZnSO4 (6-14-15). The yarn was stretched 80% in a hot bath, 2% insoi, 20% nazsoi and 4% znsoi (2-204). ,32, 33; t3 After washing, the yarns were dried, twisted, con- 4 a earbon wmet vl el ditioned, and tested at 21 0. and 60% relative 12,3 swenmg humidity. It will be seen in Table II below that 2 the addition of sodium trithiocarbonate reduced the neutralization rate, 1. e., increased the filament length at which neutralization is complete, reduced the gel swelling, and improved certain pr p It is to be understood that, beside sodium hy- Tllble II drOXide solutions, other alkaline solutions, such as cellulose ethers dissolved in aqueous potas- Hydroxyethyl Hydroxyethyl sium hydroxide, may also be used.

fig g ggg Similarly, this invention contemplates the use of trithiocarbonates other than sodium trithio 205 M1 carbonate. In general, the trithiocarbonates of 0. 50 0.65 other alkali metals and any other water soluble 1: 3 #12 m trithiocarbonates, e. g. potassium trithiocar- 33.0 23.0 bonate and lithium trithiocarbonate, may be 31 5% added to the alkaline solution of the cellulose 8.2 5.3 ethers.

This invention contemplates the use of any alkali-soluble cellulose ether. Thus, the ethers EXAMPLE m M used in the process of this invention may be of Methyl cellulose containing 5% by weight of a variety of types; for example, they may be methoxy groups was dissolved in sodium hycarboxymethyl-, hydroxyethyl, methyl-, ethyl, droxide and in trithiocarbonate-modified sodium propyl, cyanoethyl cellulose and others or mixhydroxide solutions and film were plate cast foltures thereof. Low alkyl ethers of cellulose lowing the method described in Example I. As

shown in Table III below, the sodium trithiocarbonate reduced gel swelling and the rate of neutralization. The addition of benzyltrimethylammonium hydroxide to the trithiocarbonate modified solution gives additional improvements in prepared using aliphatic alcohols having up to six carbon atoms are preferred. Others prepared using higher aliphatic alcohols may also be used, providing they are not too sparingly soluble in caustic. It is usually preferred to use ethers containing just enough ether groups to give caustic solubility. In general. the cellulose ethers contemplated here have between 0.1 and 1.0 mole of substituent group for glucose unit, preferably between 0.1 and 0.5 mole. Generally, products obtained b substituting cellulose to a high degree with ether groups are water sensitive. Thus, by limiting substitution, the water sensitivity of the,

final product is. minimized.

The alkaline solutions of the cellulose ethers may be prepared in any suitable manner and the compositions of, the solutions. may be varied widely. For example, the solution may have a cellulose ether content of from 4 to and an alkali concentration of from. 2% to 8%. While the amounts of these compositions may be higher or lower, it is preferred to use concentrations within. the ranges indicated. In general, the degree of polymerization of the cellulose ether is adjusted to give a solution viscosity of 20 to 60 poises.

The practical range of water-soluble trithiocarbonate to be added to the alkaline solutions of the cellulose ethers is from about 1%. to about 3%. Again, higher or lower amounts may be employed depending upon the result desired. The alkaline trithiocarbonate may be prepared by the reaction. of an alkali metal sulfide, such as sodium sulfide, with carbon disulfide under conditions which are controlled to give a low concentration of residual sulfide or by reacting an alkali, such as sodium hydroxide, with carbon disulfide, nder which conditions one mole of alkali metal carbonate forms for every two moles of alkali metal trithiocarbonate formed.

The basic nitrogenous modifiers suitable for i the purpose of this invention are water soluble monoamines or their alkali soluble quaternary ammonium salts, said amines or salts having at least four carbon atoms but having no radical of more than seven carbon atoms.

The quaternar ammonium compounds have the gross formula wherein X is a hydroxyl group or an anion having no surface activity, e. g., the chloride, bromide, iodide, sulfate, bisulfate, acetate, etc., anions, and the radicals R1, R2, R3 and R4, are organic groups, preferably hydrocarbon or hydroxylbearing hydrocarbon groups, at least three of these radicals being completely aliphatic and the fourth one, when aromatic, containing not more than one aromatic (benzene) nucleus. All R groups may be aliphatic and in that instance they may be alike or different. Specific examples are tetramethylammonium chloride, tetraethylammonium hydroxide, tctrahydroxyethylammonium hydroxide, tetrabutylammonium iodide, phenyltrimethylammoniu-mhydroxide, benzyltrimethylammonium chloride and hexyltrimethylammonium bromide.

The modifying amines which have been used in this invention are primary, secondary and tertiary monoamines having at least four caramyldiethanolamine, andv cyclohexylethanolamine. The corresponding quaternary ammonium salts of any of the above amines prepared using short chain aliphatic compounds such as methyl or ethyl halidesare also useful in the process of this invention. Concentrations (based on the weight of the solution or bath) of basic nitrogenous modifiers may be from about 0.2% to about 1.0%. It is preferred, however, to use them in as low concentration as. possible, e. g. 0.2% to 0.4%.

The spinning baths suitable for use in the invention contain sulfuric acid, zinc sulfate. and sodium sulfate. Zinc sulfate is an. essentialv component of the spinning bath since, in its ab.- sence, the 'trithiocarbonate or. a combination of sodium trithiocarbonate and basic nitrogen compounds have no effect on the coagulation. and spinning of films. and filaments. If desired, additional salts known. to reinforce or supplement the action. of zinc and sodiumv sulfates may be used, such as aluminum, ferrous, manganous, magnesium, and chromic sulfates. Preferably, the spinning bath contains from about 4% to about 12% sulfuric acid, from about 13% to about 25 sodium sulfate, from about. 2% to about 15% zinc sulfate, and, optionally, from about 1%. to about 15% ferrous sulfate or the other above named supplementary salts. The temperature range for best coagulation is from 40 C. to C. On the basis of available data it is desirable, in the case of filaments, for example, to have the bath acidity and temperatures as low as is practical for a given spinning speed. in order to get optimum structures and yarn properties. Each of the above concentrations should be adjusted to. each other and to the composition of the spinning solution. It is desirable to. use as high a total solids content as possible in the coagulating bath to give the highest degree of gel shrinkage and improved stretchability'.

In the process of this invention the films and filaments may be prepared in the apparatus and equipment of viscose spinning and castin known to the art. Filaments may be given a long travel of 130 to 250 inches in the primary bath by means of a multiple roller setup which gradually applies tension to the traveling filaments and thereby orients them while they are still plastic. The preferred method, however, is to apply a part or all of the stretch beyond the primary bath in a secondary bath of water, dilute bath, or concentrated bath or to use a combination of air or hot bath stretch. Stretches of 80% to are preferred for producing high tenacity yarn and trithiocarbonate and basic nitrogenous com pounds influence the spinning process is through interaction with zinc ions in the bath. It has not been possible to determine whether the effect on filament formation is accomplished through buffering action, formation of insoluble precipitates or other colloidal effects. It is known that the rate of penetration of ions and coagulation are slowed down and this probably allows greater dehydration before final gel structure is permanently set.

The coagulated articles prepared through the process of this invention can, in general, be used instead of regenerated cellulose ether fibers, films or other articles for any purpose where the latter are finding application.

--.' Any departures from the above description which conforms to the present invention is intended to be included within the scope of the claims.

I claim:

1. A method of producing cellulose ether structures which comprises the steps of adding to alkaline solutions of cellulose ethers at least 1% by weight and the said alkaline solutions of an alkali-metal trithiocarbonate and extruding the resultant solutions into aqueous sulfuric acid spinning baths containing zinc sulfate and so- .dium sulfate.

2. The process according to claim 1 in which the said structures are passed into a second bath and stretched in the said second bath.

3. The process according to claim 2 in which the said structures are stretched in saidsecond bath to an extent of at least 20%.

4. A method of producing cellulose ether structures which comprises the steps of adding to alkaline solutions of cellulose ethers at least 1% by weight of the said alkaline solutions of an alkali-metal trithiocarbonate and extruding the resultant solutions into aqueous sulfuric acid spinning baths containing from about 2% to about zinc sulfate and from about 13% to about 25% sodium sulfate.

5. A method of producing cellulose ether structures which comprises the step of extruding alkaline solutions of cellulose ethers containing at least 1% by weight of the said alkaline solutions of an alkali-metal trithiocarbonate into aqueous sulfuric acid spinning baths containing zinc sulfate and sodium sulfate, the said spinning being conducted 50 that the said structures formed thereby contact during coagulation, between 0.2% and 1.0%, based on the weight of said alkaline solution, of a basic nitrogenous modifier selected from the group consisting of alkali-soluble monoamines and their quaternary ammonium salts, the said amines and the said salts having at least four carbon atoms and having no radical containing more than seven carbon atoms.

6. A method of producing cellulose ether structures which comprises the steps of extruding into aqueous sulfuric acid spinning baths containing from about 2% to about 15% zinc sulfate and about 13% toabout 25% sodium sulfate alkaline solutions of cellulose ethers containing at least 1% of an alkali-metal trithiocarbonate and about 0.2% to about 1.0% of a basic nitrogenous modifier selected from the group consisting of alkali-soluble monoamines and their quaternary ammonium salts, the said amines and the said salts having at least four carbon atoms and containing no radical of more than seven carbon atoms.

. -'7. The process according to claim 6 in which the said structures are passed into a second-bath and stretched in the said second bath.

8. The process according to claim 7 in which the said structures are stretched in said second bath to an extent of at least r 9. A method of producing cellulose ether structures which comprises the steps of extruding alkaline solutions of cellulose ethers containing at least 1% "of an alkali-metal trithiocarbonate into aqueous sulfuric acid spinning baths containing from about 2% to about 15% zinc sulfate, about 13% to about sodium sulfate and about 0.2% to about 1.0% of a basic nitrogenous modifier selected from the group consisting of alkali-soluble monoamines and their quaternary ammonium 1 salts, the said amines and the .said'saltshaving at least four carbon atoms and containing no radical of more than seven carbon atoms.

10. The process according to claim 9 in which the said structures are passed into a second bath and stretched in the said second bath.

11. The process according to claim 10 in which the said structures :are stretched in the said second bath to an extent of at least 20%.

12. In a method of producing cellulose ether structures by extruding alkali solutions of cellulose ethers into aqueous sulfuric acid coagulating baths containing from about 2% to about 15% zinc sulfate and about 13% to about 25% sodium sulfate, the step which comprises adding to the said alkaline solutions of the said cellulose ethers at least 1% of an'alkali-metal trithiocarbonate.

13. In a method of producing cellulose ether structures by extruding alkaline solutions of cellulose ethers into aqueous sulfuric acid coagulating baths containing from about 2% to about 15% zinc sulfate and about 13% to about 25% sodium sulfate, the step which comprises incorporating in the said alkaline solutions of the said cellulose ethers at least 1% of an alkalimetal trithiocarbonate and about 0.2% to about 1.0% of a basic nitrogenous modifier selected from the group consisting of alkali-soluble monoamines and their alkali-soluble quaternary ammonium salts, the said amines and the said salts having at least four carbon atoms but having no radical of more than'seven carbon atoms.

14; In a method of producing cellulose ether structures by extruding alkaline solutions of cellulose ethers into aqueous sulfuric acid coagulating baths containing from about 2% to about 15% zinc sulfate and about 13% to about 25% sodium sulfate, the steps which comprise incorporating in the said alkaline solutions of the said cellulose ethers at least 1% of an alkalimetal trithiocarbonate and incorporating into the said aqueous sulfuric acid spinning baths about 0.2% to about 1.0% of a basic nitrogenous modifier selected from the group consisting of alkali-soluble monoamines and their alkali-soluble ammonium salts, the said amines and the said salts having at least four carbon atoms but having no radical of more than seven carbon atoms.

15. A process which comprises adding to alkaline solutions of cellulose ethers at least 1% of an alkali-metal trithiocarbonate and extruding the resultant solutions into a coagulating bath comprising an aqueous solution of about 4% to about 12% sulfuric acid, about 13% to about 25% sodium sulfate and about 2% to about 15% zinc sulfate.

16. A process which comprises incorporating in alkaline solutions of cellulose ethers at least 1% of an alkali-metal trithiocarbonate and about 0.2% to about 1.0% of a basic nitrogenous modifier and extruding the resultant solutions into a coagulating bath comprising-an aqueous solution of about 4% to about 12% sulfuric acid,

, about 13% to about 25% sodium sulfate and in alkali solutions of cellulose ethers at least 1% of an alkali-metal trithiocarbonate and BXtIlJ-dr ing the resultant solutions into a coagulating bath comprising an aqueous solution of about 4% to about 12% sulfuric acid, about 13% to about 25% sodium sulfate, about 2% to about 15% zinc sulfate and about 0.2% toabout 1.0% of a basic nitrogenous modifier selected from the group consisting of alkali-soluble monoamines and their quaternary ammonium salts, the said amines and the said salts having at least four carbon atoms but having no radical of more than seven carbon atoms.

'18. An alkaline solution of a cellulose ether derived from an aliphatic alcohol having up to six carbon atoms, said solution containing at least 1% of an alkali-metal trithiocarbonate and about 0.2% to about 1.0% of a basic nitrogenous modifier selected from the group consisting of alkali-soluble monoamines and their quaternary ammonium salts, the said amines and the said salts having at least four carbon atoms but having no radical of more than seven carbon atoms.

19. An alkaline solution of a cellulose ether derived from an aliphatic alcohol having up to six carbon atoms, said solution containing from the said amines and the said salts having at least four carbon atoms but having no radical of more than seven carbon atoms.

20. An alkaline solution of a cellulose ether derived from an aliphatic alcohol having up to six carbon atoms, said solution containing from 1% to 3% of an alkali metal trithiocarbonate and about 0.2% to about 1.0% of a basic nitrogenous modifier selected from the group consisting of alkali-soluble monoamines and their quaternary ammonium salts, the said amines and the said salts having at least four carbon atoms but having no radical of more than seven carbon atoms.

21. An alkaline solution of a cellulose ether derived from an aliphatic alcohol having up to six carbon atoms, said solution containing from about 4% to about 10% of said cellulose ether and from about 2% to about 8% of an alkali and from 1% to 3% of an alkali metal trithiocarbonate and about 0.2% to about 1.0% of a basic nitrogenous modifier selected from the group consisting of alkali-soluble monoamines and their alkali-soluble quaternary ammonium salts, the said amines and the said salts having at least four carbon atoms but having no radical of more than seven carbon atoms.

NORMAN LOUIS COX.

REFERENCES CITED The following references are of record'in the file of this patent:

UNITED STATES PATENTS Number Name a Date 2,288,413 Morgan June 30, 1942 2,301,509 Bock 1 Nov. 10, 1942 2,301,676 Balle Nov. 10, 1942 2,304,252 Hager Dec. 8, 1942 2,310,208 Bley Feb. 9, 1943 2,310,969 Lilienfeld Feb. 16, 1943 2,373,712 Schlosser Apr. 17, 1945 2,412,969 Cramer Dec. 24, 1946 FOREIGN PATENTS Number Country Date 778,947 France Mar. 26, 1935 OTHER REFERENCES Berl et al., Cellulose Chemie VII, Oct. 31, 1926, page 138, col. 1, 2nd paragraph. 

1. A METHOD OF PRODUCING CELLULOSE ETHER STRUCTURES WHICH COMPRISES THE STEPS OF ADDING TO ALKALINE SOLUTIONS OF CELLULOSE ETHERS AT LEAST 1% BY WEIGHT AND THE SAID ALKALINE SOLUTIONS OF AN ALKALI-METAL TRITHIOCARBONATE AND EXTRUDING THE RESULTING SOLUTIONS INTO AQUEOUS SULFURIC ACID SPINNING BATHS CONTAINING ZINC SULFATE AND SODIUM SULFATE. 